1. Field of the Invention
The present invention relates to a method for manufacturing cathodes, and a method for manufacturing electron sources, electron beam generating apparatuses, and image forming apparatuses such as flat-panel displays.
2. Description of the Related Art
There are two types of cathodes (electron-emitting devices) that have been conventionally known; thermionic cathodes, and cold cathodes. Cold cathodes include field-emission types (hereafter referred to as xe2x80x9cFE-typexe2x80x9d), and metal layer/insulating layer/metal layer types (hereafter referred to as xe2x80x9cMIM-typexe2x80x9d) and surface conduction type cathodes.
Examples of surface conduction type cathodes are disclosed in Japanese Patent Laid-Open No. 8-55563, Japanese Patent Laid-Open No. 7-235255, Japanese Patent Laid-Open No. 8-007749, Japanese Patent Laid-Open No. 8-321254, Japanese Patent No. 2836015, Japanese Patent Laid-Open No. 9-237571, Japanese Patent Laid-Open No. 7-65704, Japanese Patent Laid-Open No. 10-40807, Japanese Patent Laid-Open No. 8-171850, Japanese Patent Laid-Open No. 9-069334, and so forth.
FIG. 12 schematically illustrates an example of the configuration of a surface conduction type cathode, disclosed in the above Japanese Patent Laid-Open No. 8-321254. In the Figure, reference numeral 1 denotes a substrate, 2 and 3 denote electrodes, 4 denotes an electroconductive film, 5 denotes an electron emission portion, and 10 denotes a carbon film. The area near the electron emission portion 5 is formed of a first gap 6 which defines the gap in the electroconductive film, and a second gap 7 which defines the gap in the carbon film 10. The gap L shown in the Figure is set at several tens of xcexcm to several hundred xcexcm, the width W at several xcexcm to several hundred xcexcm, and the thickness d at several tens of xcexcm to several hundred xcexcm.
Also, FIG. 13 illustrates an example of the method of manufacturing a conventional surface conduction type cathode, such-as disclosed in the above Japanese Patent Laid-Open No. 8-321254.
First, electrodes 2 and 3 are positioned on the substrate 1 (FIG. 13A). Then, an electroconductive film 4 for connecting the electrodes 2 and 3 is positioned (FIG. 13B). Next, flowing a current through the electroconductive film 4 forms a first gap 6 at a portion of the electroconductive film (FIG. 13C). The process of forming this first gap 6 in the electroconductive film is called xe2x80x9cformingxe2x80x9d or xe2x80x9cenergization formingxe2x80x9d. Next, the carbon film 10 is formed by, for example, introducing an organic gas in a vacuum, and applying voltage between the two electrodes 2 and 3 in this atmosphere (FIG. 13D). Incidentally, the second gap 7 is formed at the same time as forming this carbon film 10. The process of forming the carbon film 10 and the second gap 7 is called xe2x80x9cactivationxe2x80x9d. The area near the second gap 7 formed by this activation process is called the electron emission portion 5.
There have been the following problems with the above-described conventional activation process.
Firstly, in the case of forming the carbon film from organic material gas, there have been the following problems. There is the need to introduce the organic material gas at an optimal gas pressure for the above activation process. Particularly, depending on the type of organic material gas that is to be introduced, there has been problems in pressure controllability in the event that the optimal gas pressure is low. Also, there have been cases wherein the amount of time necessary for the activation process changes or the nature of the formed carbon film differs due to residual water, oxygen, or the like in the vacuum atmosphere. This has caused irregularities in the electron emission properties of electron sources or image forming apparatuses.
Secondly, in the event of using the aforementioned cathodes for image forming apparatuses or electron sources, there have been the following problems. That is following the activation process, the gas used on the activation process, and also water, oxygen, etc., have adhered to the substrate for the electron source, or member comprising the image forming apparatus, e.g., a face plate having fluorescent material. Accordingly, there is the need to remove the gas and the like adhering thereto, to stabilize electron emission properties. To this end, conventional arrangements required a process called xe2x80x9cstabilizingxe2x80x9d, wherein the substrate on which the electron-emitting devices are arrayed, or the air-tight container enveloping the devices, are baked at high temperatures for long periods of time. With this stabilizing process, the higher the temperature, the better; and the longer the time, the better. However, in practice, the stabilizing process is restricted regarding the heating temperature due to the heat-resistance properties of the members comprising the cathodes, electron sources, and image forming apparatuses, so sufficient heating has not always been able to be performed.
Thirdly, in the sealing process for fabricating image forming apparatuses, there have been the following problems. That is, in the case of fabricating image forming apparatuses, conventional arrangements involved bonding together at high temperatures an electron source substrate comprising wires and the like for driving each device with a face plate having fluorescent material or the like, thereby forming an envelope (referred to as the sealing process). Then, following this sealing process, voltage is applied from the wires, the aforementioned forming and activating processes and the like are performed. In this way, the forming and activating processes are performed after the image forming apparatus (vacuum envelope) is assembled, so in the event that a defect occurs on the electron source substrate due to one reason or another, the entire image forming apparatus becomes defective. Accordingly, an arrangement has been awaited wherein the forming and activating processes are performed, and inspected, following which the electron source substrate which has passed the inspection and the face plate are assembled to manufacture the image forming apparatus.
Fourthly, the above Japanese Patent Laid-Open No. 9-237571 discloses a manufacturing method which is said to solve the above problems, but means for realizing further reductions in costs has been awaited.
Accordingly, the present invention has achieved the above objectives, by the following manufacturing methods.
According to an aspect of the present invention, a method for manufacturing a cathode comprises the steps of:
A) a process for applying onto a substrate a fluid mixture comprising polymers or precursors to the polymers, fine particles of electroconductive material or organic metal compound, and solvent;
B) a process for removing the solvent by heating the fluid mixture applied on the substrate, thereby obtaining an electroconductive organic film comprising the polymers and the electroconductive material; and
C) a process for forming a gap at a portion of the electroconductive organic film by flowing a current through the film.
Now, the process for applying the fluid mixture according to the present invention may be performed by the ink-jet method, and the ink-jet method may involve applying heat to the fluid mixture to the point of boiling so as to generate bubbles, thereby using the pressure of the bubbles to eject droplets of the fluid mixture.
Also, according to the present invention, the ink-jet method may involve applying electric signals to piezoelectric elements so as to cause deformation thereof, thereby ejecting droplets of the fluid mixture.
The polymers may comprise at least one selected from the following group: all-aromatic polymers, and polyacryllo nitryl. Here, the all-aromatic polymer may comprise one of polyimide, polybenzoimidazole, and polyamideimide.
The electroconductive material according to the present invention may comprise at least one selected from the following group: Pd, Ru, Ag, Cu, Tb, Cd, Fe, Pb, Zn, PdO, SnO2, In2O3, PbO, Sb2O3, HfB2, ZrB2, LaB6, CeB6, YB4, GdB2, TiC, ZrC, HfC, TaC, SiC, WC, TiN, ZrN, HfN, polyacetylene, poly-p-phenylene, polyphenylene sulfide, polypyrrole, Si, Ge, carbon, and graphite.
Also, the electroconductive material may comprise at least one selected from the following group: metals, oxides, borides, carbides, nitrides, electroconductive polymers, and semiconductors.
According to another aspect of the present invention, a method for manufacturing a cathode comprises the steps of:
A) a step for forming on a substrate an electroconductive organic film comprising a mixture of:
at least one organic material selected from the following group: all-aromatic polymers, and polyacryllo nitrile; and
an electroconductive material; and
B) a step for forming a gap at a portion of the electroconductive organic film by flowing a current through the film.
According to yet another aspect of the present invention, a method for manufacturing a cathode comprises the steps of:
A) a step for forming on a substrate an electroconductive film comprising:
at least one organic material selected from the following group: all-aromatic polymers, and polyacryllo nitrile; and
an electroconductive material; and
B) a step for forming a gap at a portion of the electroconductive organic film by flowing a current through the film.
The all-aromatic polymers here may comprise at least one organic material selected from the following group: polyimide, polybenzoimidazole, and polyamideimide.
According to a further aspect of the present invention, a method for manufacturing a cathode comprises the steps of:
A) a step for forming an electroconductive organic film on a substrate layer; and
B) a step for forming a gap at a portion of the electroconductive organic film by flowing a current through the film.
According to another aspect of the present invention, a method for manufacturing an electron source comprising an array of a plurality of cathodes uses cathodes which are manufactured according to any of the methods described above.
The method for manufacturing the above electron source comprises:
A) a step for forming an array of a plurality of pairs of electrodes on a substrate, using offset printing;
B) a step for forming a plurality of X-directional wires coming into common contact with one of the pair of electrodes, on the substrate using screen printing;
C) a step for forming a plurality of Y-directional wires coming into common contact with the other of the pair of electrodes, on the substrate using screen printing;
D) a step for positioning the electroconductive organic film so as to connect between each of the pairs of electrodes, using the ink-jet method; and
E) a process for forming a gap at a portion of the electroconductive organic film by flowing a current through the film, via the X-directional wires and the Y-directional wires.
Here, the Y-directional wires are formed over the X-directional wires so as to be electrically insulated therefrom by an insulating layer formed using screen printing, and the Y-direction and the X-direction are substantially perpendicular.
According to yet another aspect of the present invention, the electron source in a method for manufacturing an image forming apparatus comprising an electron source having an array of a plurality of cathodes and image forming members positioned facing the electron source is manufactured according to the aforementioned method for manufacturing electron sources.
Thus, according to the present invention, firstly, control of the pressure of the organic gas being introduced is not necessary as with conventional methods for manufacturing cathodes, the effects of the residual gas in the vacuum atmosphere are relieved, and electron emission properties can be readily controlled.
Also, secondly, with the method for manufacturing cathodes according to the present invention, electron emission portion can be formed to the electroconductive film using heat due to application of electricity or electric energy. Thus, the electron emission properties can easily be controlled according to the power at forming process and/or the thickness of the electroconductive organic film. Accordingly, in the case of manufacturing electron sources or image forming apparatuses wherein a plurality of cathodes are arrayed, control of the electron emission properties can be readily conducted as compared to the activation process of conventional arrangements which require control of the organic gas, providing a simpler process. Consequently, irregularities in electron emission properties can be suppressed.
Also, thirdly, electron sources which have passed inspection and face plates which have passed inspection can be used for the assembly process (bonding process), so the occurrence of defects after assembly of the image forming apparatus can be reduced as compared to the activation process of conventional arrangements which require control of the organic gas. Consequently, the cost of the image forming apparatus can be reduced.
Further, fourthly, with the manufacturing method according to the present invention, there is no need to align the electroconductive film and the organic film as with the conventional manufacturing method wherein the organic film covers the electroconductive film, disclosed in Japanese Patent Laid-open No. 9-237571. Accordingly, defective cathodes and irregularity in electron emission properties owing to offset of the carbon film can be suppressed, thereby providing cathodes with excellent electron emission properties. Further, using the ink-jet method to form organic film having electroconductivity according to the present invention reduces the patterning process for the device, thereby reducing costs. Moreover, forming the electrodes forming the cathodes and the wires for driving the cathodes by printing enables all components of the cathodes and electron sources to be formed by printing processes, realizing even further reductions in costs.